The goal of this proposal is to develop a prototype intraoperative beta camera (IOBC) specifically designed for use in imaging beta emitting radiopharmaceuticals (such as 18F, 124I, 186Re, and 188Re) incorporated into tumors in the brain or other organs such as breast, lymph nodes, thyroid and others. The probe is intended for use in the intraoperative surgical environment. The patient is injected with a tumor seeking radiopharmaceutical before surgery, the surgical procedure to remove tumor mass is performed, and the site is then imaged using the IOBC probe to locate residual subclinical tumor cells. The proposed system is intended to significantly improve the success of tumor removal surgeries by allowing more complete removal of subclinical tumor cells without excessive removal of normal tissue. The intraoperative beta camera will use a small, and light-weight, detachable head comprising a 256-pixel silicon-PIN array which is highly sensitive to beta particles but insensitive to the noisy gamma background radiation. During the Phase I feasibility study we will construct a 256-pixel prototype of the array and characterize its performance in terms of electronic noise, spatial resolution, sensitivity, and uniformity of response to beta emitters. In addition, optimization of amplification electronics will be done to assure required high degree of miniaturization and sufficiently low electronic noise. In Phase II a complete intraoperative imaging system including miniaturized detector probe, processing electronics, data collection, image processing and display hardware and software will be designed and developed. PROPOSED COMMERCIAL APPLICATION There is a need for commercial intraoperative imaging cameras to improve the success of tumor removal surgeries. This could significantly reduce time in surgery with a commensurate decrease in cost of surgeries. This could significantly reduce time in surgery with a commensurate decrease in cost of surgery and leading to faster recovery and lower recovery cost. The proposed work is focused on a novel semiconductor beta camera system with detachable, compact, and lightweight imaging probe. Different versions of the probe could be adapted for breast, lymph nodes, thyroid, and other organs.